Ali H. Soufan, a former F.B.I. counterterrorism specialist who has interrogated some of the most hardened jihadists the world has ever known, is one of America’s premier experts on Al Qaeda. So when he writes that the Islamic State will have a difficult time maintaining its relevance once its caliphate collapses, his message should be taken seriously.

But we shouldn’t necessarily bank on ISIS losing its luster. There’s no question that the organization’s appeal will diminish a great deal once Mosul and Raqqa are inevitably recaptured by the United States-backed Iraqi Army and Syrian Democratic Forces, respectively. Its recruitment power may very well go down, and its moneymaking will dry up to an even larger extent.

Terrorist groups, however, don’t necessarily require a territorial safe haven to plot and conduct mass casualty attacks. The two brothers who perpetrated the 2016 suicide bombings in Brussels were first-generation Belgians of Moroccan descent who reportedly never traveled to Syria in their lives. Instead, they were radicalized in prison.

The lesson here is straightforward: As long as the Islamic State has access to a laptop and secure social media apps, all it needs to do is inspire its sympathizers to violence. No territory required.